This invention relates to a switch of the type wherein a movable contact is operated by a coil spring.
A typical one of conventional switches of this type has a structure as shown in FIG. 1. Referring first to FIG. 1, the switch includes a switch body 1 which has a center terminal 2 and a fixed contact terminal 3 secured thereto. The center terminal 2 has a recessed portion 5 adjacent an upright portion 4 thereof, and an end 7 of an operating lever 6 is pivotally mounted on the recessed portion 5 of the center terminal 2. An operating member 8 is mounted for sliding movement into and out of the switch body 1, and when pushed in, an end 9 thereof pushes the other end 10 of the operating lever 6 inwardly. A movable contact receiving recess 12 is formed in an upright portion 11 of the operating lever 6 which portion 11 serves as a movable part of the lever 6. A movable contact member 13 is pivotally received in the recess 12 of the operating lever 6 so that it can be rocked about a movable fulcrum provided by the recess 12. A movable contact 15 is formed on one of opposite surfaces of a rocking end of the movable contact member 13 and is opposed to a fixed contact 16 of the fixed contact terminal 3. The movable contact member 13 further has a spring mounting portion 17 between the movable contact 15 and the end 14 thereof, and an end of a tension spring 18 is connected to the spring mounting portion 17. The other end 20 of the tension spring 18 is secured to a spring mounting portion 21 of the center terminal 2 and thus integrally secured to the switch body 1 to urge the movable contact member 13 to move the movable contact 15 thereof toward the recess 12 of the operating lever 6. FIG. 1(A) shows the switch in a stable open position, and in this position, a stop 22 provided on the center terminal 2 is abutted by the operating lever 6 to stop and limit movement of the operating lever 6 toward the operating member 8. Further, in this position, the end 14 of the movable contact member 13 which serves as a movable fulcrum of the movable contact member 13 is located, in FIG. 1(A), on the right side of a line of action which interconnects opposite ends 19, 20 of the tension spring 18. As a result, the movable contact member 13 is urged by a clockwise rocking moment due to the tensile force of the tension spring 18 and hence a rear face 23 of the movable contact member 13 is abutted against a side wall 24 of the switch body 1 which side wall 24 serves as a disengagement limiting member of the switch.
In such a construction as described above, however, when the operating member 8 is pushed in, the operating lever 6 is pivoted thereby and the end 14 of the movable contact member 13 is first moved to the line of action of the tension spring 18 as shown in FIG. 1(B) and then is further moved across the line of action whereupon the movable contact member 13 is rocked counterclockwise about the end 14 thereof by the urging of the tension spring 18 until the movable contact 15 is contacted with the fixed contact 16 as shown in FIG. 1(C). During this operation, relative positions between the contacts 15, 16 when the switch is in the position as shown in FIG. 1(B) at which rocking moment is reversed are similar to those when the switch is in the position as shown in FIG. 1(A), and thus the contacts 15, 16 are spaced from each other a relatively large distance. Accordingly, acceleration of the movable contact 15 at the instant when it is contacted with the fixed contact 16 is naturally relatively high, causing rebounding of the movable contact member 13 upon contacting of the movable contact 15. As a result, sparks are naturally large and will cause a problem that the contacts 15, 16 suffer from serious corrosion and wear which will reduce the life of the contacts.